A key debate in demographic history revolves around whether mortality declined during the nineteenth and early twentieth centuries in the West because of the purposive actions taken by medical practitioners, public health officials and individuals or simply as one of many offshoots of the process of industrialization and the general rise in per capita income. This proposal addresses itself to this debate by focussing on a case study of the role of the municipal government in the decline in mortality in Philadelphia from 1870 to 1930. A number of municipal services, notably supplying the city with adequate and clean water, isolating and quarantining ill citizens, cleaning up slums, providing a pure milk supply, vaccinating citizens against smallpox and making available particular treatments in municipal hospitals were undertaken during that time period. My aim in the proposed research is to examine the effect that specific activities and activists in Philadelphia had on mortality levels. The analysis uses a two step approach. First age- and cause- specific mortality rates will be examined to determine the cause of death responsible for the overall decrease in the probabilities of dying at any age. In addition, mortality levels will be determined for a number of ethnic groups and geographic subareas in the city. In a second stage of the analysis, the activities directed at reducing mortality levels are related to changes in age- , cause- and subgroup- specific mortality levels. The proposed monograph growing out of this analysis will add to the work being done by both demographers and medical and public health historians and will make a contribution to the substantive problem of explaining the decline in mortality. The former have concentrated on outlining the mortality transition, the latter on the growth of activities directed at reducing mortality levels. My purpose is to show the overlap between these two often separated spheres of research.